Handle LastRenderedPageBreak in RunUtil

Add handling for R.LastRenderedPageBreak in the RunUtil class to return an empty string. This ensures that when LastRenderedPageBreak is encountered, no extraneous characters are output, maintaining the integrity of the generated content.

engine/src/main/java/pro/verron/officestamper/core/RunUtil.java

@@ -67,6 +67,7 @@ public static CharSequence getText(Object content) {
         if (content instanceof Br br && br.getType() == STBrType.COLUMN) return "\n";
         if (content instanceof R.NoBreakHyphen) return "‑";
         if (content instanceof R.SoftHyphen) return "\u00AD";
+        if (content instanceof R.LastRenderedPageBreak) return "";
         if (content instanceof R.Sym sym) return "<sym(" + sym.getFont() + ", " + sym.getChar() + ")>";
 
         log.debug("Unhandled object type: {}", content.getClass());